// Copyright 2017 clair authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package pgsql implements database.Datastore with PostgreSQL.
package pgsql

import (
	"database/sql"
	"fmt"
	"io/ioutil"
	"net/url"
	"strings"
	"time"

	"gopkg.in/yaml.v2"

	"github.com/hashicorp/golang-lru"
	"github.com/lib/pq"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/remind101/migrate"
	log "github.com/sirupsen/logrus"

	"github.com/coreos/clair/database"
	"github.com/coreos/clair/database/pgsql/migrations"
	"github.com/coreos/clair/pkg/commonerr"
	"github.com/coreos/clair/pkg/pagination"
)

var (
	promErrorsTotal = prometheus.NewCounterVec(prometheus.CounterOpts{
		Name: "clair_pgsql_errors_total",
		Help: "Number of errors that PostgreSQL requests generated.",
	}, []string{"request"})

	promCacheHitsTotal = prometheus.NewCounterVec(prometheus.CounterOpts{
		Name: "clair_pgsql_cache_hits_total",
		Help: "Number of cache hits that the PostgreSQL backend did.",
	}, []string{"object"})

	promCacheQueriesTotal = prometheus.NewCounterVec(prometheus.CounterOpts{
		Name: "clair_pgsql_cache_queries_total",
		Help: "Number of cache queries that the PostgreSQL backend did.",
	}, []string{"object"})

	promQueryDurationMilliseconds = prometheus.NewHistogramVec(prometheus.HistogramOpts{
		Name: "clair_pgsql_query_duration_milliseconds",
		Help: "Time it takes to execute the database query.",
	}, []string{"query", "subquery"})

	promConcurrentLockVAFV = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "clair_pgsql_concurrent_lock_vafv_total",
		Help: "Number of transactions trying to hold the exclusive Vulnerability_Affects_Feature lock.",
	})
)

func init() {
	prometheus.MustRegister(promErrorsTotal)
	prometheus.MustRegister(promCacheHitsTotal)
	prometheus.MustRegister(promCacheQueriesTotal)
	prometheus.MustRegister(promQueryDurationMilliseconds)
	prometheus.MustRegister(promConcurrentLockVAFV)

	database.Register("pgsql", openDatabase)
}

// pgSessionCache is the session's cache, which holds the pgSQL's cache and the
// individual session's cache. Only when session.Commit is called, all the
// changes to pgSQL cache will be applied.
type pgSessionCache struct {
	c *lru.ARCCache
}

type pgSQL struct {
	*sql.DB

	cache  *lru.ARCCache
	config Config
}

type pgSession struct {
	*sql.Tx

	key pagination.Key
}

// Begin initiates a transaction to database.
//
// The expected transaction isolation level in this implementation is "Read
// Committed".
func (pgSQL *pgSQL) Begin() (database.Session, error) {
	tx, err := pgSQL.DB.Begin()
	if err != nil {
		return nil, err
	}
	return &pgSession{
		Tx:  tx,
		key: pagination.Must(pagination.KeyFromString(pgSQL.config.PaginationKey)),
	}, nil
}

func (tx *pgSession) Commit() error {
	return tx.Tx.Commit()
}

// Close closes the database and destroys if ManageDatabaseLifecycle has been specified in
// the configuration.
func (pgSQL *pgSQL) Close() {
	if pgSQL.DB != nil {
		pgSQL.DB.Close()
	}

	if pgSQL.config.ManageDatabaseLifecycle {
		dbName, pgSourceURL, _ := parseConnectionString(pgSQL.config.Source)
		dropDatabase(pgSourceURL, dbName)
	}
}

// Ping verifies that the database is accessible.
func (pgSQL *pgSQL) Ping() bool {
	return pgSQL.DB.Ping() == nil
}

// Page is the representation of a page for the Postgres schema.
type Page struct {
	// StartID is the ID being used as the basis for pagination across database
	// results. It is used to search for an ancestry with ID >= StartID.
	//
	// StartID is required to be unique to every ancestry and always increasing.
	StartID int64
}

// Config is the configuration that is used by openDatabase.
type Config struct {
	Source    string
	CacheSize int

	ManageDatabaseLifecycle bool
	FixturePath             string
	PaginationKey           string
}

// openDatabase opens a PostgresSQL-backed Datastore using the given
// configuration.
//
// It immediately runs all necessary migrations. If ManageDatabaseLifecycle is
// specified, the database will be created first. If FixturePath is specified,
// every SQL queries that are present insides will be executed.
func openDatabase(registrableComponentConfig database.RegistrableComponentConfig) (database.Datastore, error) {
	var pg pgSQL
	var err error

	// Parse configuration.
	pg.config = Config{
		CacheSize: 16384,
	}
	bytes, err := yaml.Marshal(registrableComponentConfig.Options)
	if err != nil {
		return nil, fmt.Errorf("pgsql: could not load configuration: %v", err)
	}
	err = yaml.Unmarshal(bytes, &pg.config)
	if err != nil {
		return nil, fmt.Errorf("pgsql: could not load configuration: %v", err)
	}

	if pg.config.PaginationKey == "" {
		panic("pagination key should be given")
	}

	dbName, pgSourceURL, err := parseConnectionString(pg.config.Source)
	if err != nil {
		return nil, err
	}

	// Create database.
	if pg.config.ManageDatabaseLifecycle {
		log.Info("pgsql: creating database")
		if err = createDatabase(pgSourceURL, dbName); err != nil {
			return nil, err
		}
	}

	// Open database.
	pg.DB, err = sql.Open("postgres", pg.config.Source)
	if err != nil {
		pg.Close()
		return nil, fmt.Errorf("pgsql: could not open database: %v", err)
	}

	// Verify database state.
	if err = pg.DB.Ping(); err != nil {
		pg.Close()
		return nil, fmt.Errorf("pgsql: could not open database: %v", err)
	}

	// Run migrations.
	if err = migrateDatabase(pg.DB); err != nil {
		pg.Close()
		return nil, err
	}

	// Load fixture data.
	if pg.config.FixturePath != "" {
		log.Info("pgsql: loading fixtures")

		d, err := ioutil.ReadFile(pg.config.FixturePath)
		if err != nil {
			pg.Close()
			return nil, fmt.Errorf("pgsql: could not open fixture file: %v", err)
		}

		_, err = pg.DB.Exec(string(d))
		if err != nil {
			pg.Close()
			return nil, fmt.Errorf("pgsql: an error occurred while importing fixtures: %v", err)
		}
	}

	// Initialize cache.
	// TODO(Quentin-M): Benchmark with a simple LRU Cache.
	if pg.config.CacheSize > 0 {
		pg.cache, _ = lru.NewARC(pg.config.CacheSize)
	}

	return &pg, nil
}

func parseConnectionString(source string) (dbName string, pgSourceURL string, err error) {
	if source == "" {
		return "", "", commonerr.NewBadRequestError("pgsql: no database connection string specified")
	}

	sourceURL, err := url.Parse(source)
	if err != nil {
		return "", "", commonerr.NewBadRequestError("pgsql: database connection string is not a valid URL")
	}

	dbName = strings.TrimPrefix(sourceURL.Path, "/")

	pgSource := *sourceURL
	pgSource.Path = "/postgres"
	pgSourceURL = pgSource.String()

	return
}

// migrate runs all available migrations on a pgSQL database.
func migrateDatabase(db *sql.DB) error {
	log.Info("running database migrations")

	err := migrate.NewPostgresMigrator(db).Exec(migrate.Up, migrations.Migrations...)
	if err != nil {
		return fmt.Errorf("pgsql: an error occurred while running migrations: %v", err)
	}

	log.Info("database migration ran successfully")
	return nil
}

// createDatabase creates a new database.
// The source parameter should not contain a dbname.
func createDatabase(source, dbName string) error {
	// Open database.
	db, err := sql.Open("postgres", source)
	if err != nil {
		return fmt.Errorf("pgsql: could not open 'postgres' database for creation: %v", err)
	}
	defer db.Close()

	// Create database.
	_, err = db.Exec("CREATE DATABASE " + dbName)
	if err != nil {
		return fmt.Errorf("pgsql: could not create database: %v", err)
	}

	return nil
}

// dropDatabase drops an existing database.
// The source parameter should not contain a dbname.
func dropDatabase(source, dbName string) error {
	// Open database.
	db, err := sql.Open("postgres", source)
	if err != nil {
		return fmt.Errorf("could not open database (DropDatabase): %v", err)
	}
	defer db.Close()

	// Kill any opened connection.
	if _, err = db.Exec(`
    SELECT pg_terminate_backend(pg_stat_activity.pid)
    FROM pg_stat_activity
    WHERE pg_stat_activity.datname = $1
    AND pid <> pg_backend_pid()`, dbName); err != nil {
		return fmt.Errorf("could not drop database: %v", err)
	}

	// Drop database.
	if _, err = db.Exec("DROP DATABASE " + dbName); err != nil {
		return fmt.Errorf("could not drop database: %v", err)
	}

	return nil
}

// handleError logs an error with an extra description and masks the error if it's an SQL one.
// The function ensures we never return plain SQL errors and leak anything.
// The function should be used for every database query error.
func handleError(desc string, err error) error {
	if err == nil {
		return nil
	}

	if err == sql.ErrNoRows {
		return commonerr.ErrNotFound
	}

	log.WithError(err).WithField("Description", desc).Error("Handled Database Error")
	promErrorsTotal.WithLabelValues(desc).Inc()

	if _, o := err.(*pq.Error); o || err == sql.ErrTxDone || strings.HasPrefix(err.Error(), "sql:") {
		return database.ErrBackendException
	}

	return err
}

// isErrUniqueViolation determines is the given error is a unique contraint violation.
func isErrUniqueViolation(err error) bool {
	pqErr, ok := err.(*pq.Error)
	return ok && pqErr.Code == "23505"
}

// observeQueryTime computes the time elapsed since `start` to represent the
// query time.
// 1. `query` is a pgSession function name.
// 2. `subquery` is a specific query or a batched query.
// 3. `start` is the time right before query is executed.
func observeQueryTime(query, subquery string, start time.Time) {
	promQueryDurationMilliseconds.
		WithLabelValues(query, subquery).
		Observe(float64(time.Since(start).Nanoseconds()) / float64(time.Millisecond))
}